.box1 {
    width: 100px;
    height: 100px;
    background-image: url('../images/1.jpeg');
}

.box2 {
    width: 100px;
    height: 100px;
    background-image: url('../images/2.png');
}

.box3 {
    width: 100px;
    height: 100px;
    background-image: url('../images/3.gif');
}